As a conventional heating system for vehicles, a hot-water heater is mostly used which provides heating for a vehicle interior by utilizing an engine coolant heated to a high temperature. Unexamined Japanese Patent Publication No. H10-076837 discloses an air conditioning device for vehicle that basically uses the existing hot-water heater and can enhance heating performance in comparison with an existing device by additionally including a configuration for using a heat pump to heat a coolant of the hot-water heater. The air conditioning device for vehicle in Unexamined Japanese Patent Publication No. H10-076837 is configured such that a coolant for cooling an engine is circulated through a condenser, a heater core, and an evaporator in this order in series, and fed back into the engine. The air conditioning device for vehicle in Unexamined Japanese Patent Publication No. H10-076837 enhances the heating performance by further heating the engine coolant in the condenser with a refrigerant discharged from a compressor.